This invention relates to telechelic silicone polymers. In particular, this invention relates to telechelic organopolysiloxanes having multiple cationic polymerizable end groups such as epoxy, vinyl ether, or propenyl ether end groups, and to methods for synthesis of the same.
Telechelic polymers are terminally-functionalized, macromolecular polymers. Silicone polymers (organopolysiloxanes) having epoxy and/or vinyl ether functional groups are of particular utility in curable compositions to produce release coatings, that is, coatings which release materials that would ordinarily be adherent. Such materials include pressure-sensitive adhesives for labels, decorative laminates, transfer tapes, and the like.
One common approach to manufacture of organopolysiloxane release coatings is based on hydrosilation of vinyl-terminated polysiloxanes with hydride crosslinkers. Another approach is based on photocatalyzed cross-linking of epoxy-functional organopolysiloxanes. U.S. Pat. Nos. 4,208,503, 4,421,904, 4,640,967, 5,187,251, and 5,217,805, for example, describe epoxy-functional polysiloxanes useful for the preparation of release coatings. These polysiloxanes contain the epoxy functionality located on the polymer ends and/or randomly distributed on the siloxane backbone. These polymers are then mixed with a photo-catalyst such as diaryliodonium hexafluoroantimonate, and cured by an irradiation with UV light to provide a release coating.
The major disadvantage of epoxy-based release coatings over those made by the hydrosilation of vinyl-terminated polysiloxanes is their brittleness. The brittleness of epoxy-functional systems is related to the presence of relatively short segments of dimethylsiloxane units (usually from 5 to 20 dimethylsiloxane units) between crosslinked islands of organic polyethers which have high glass transition temperature. In an attempt to solve this problem, epoxy end-stopped siloxane polymers have been manufactured having 100 or more dimethylsiloxane units between the epoxy functionalized groups. Cure of such polymers results in flexible coatings, but such systems suffer from a very low activity (very slow cure). Slow cure severely limits practical use of such long-chain siloxane polymers.
Accordingly, there remains a continuing need in the art for new functionalized siloxane polymers with both improved cure activity and improved release coating properties upon cure.